A 6-year-old girl developed early puberty because she often played with shopping receipts? Is it okay to touch thermal paper?

Some time ago, a piece of news shocked Tadpole: According to Life Times Weibo, a Spanish website reported that a 6-year-old girl showed symptoms of precocious puberty because she often played with shopping receipts at home.

Supermarket receipts are made of thermal paper, and many of the papers we use in our daily lives, such as movie tickets, lottery tickets and other paper products, are also made of thermal paper.

The shopping receipt is made of thermal paper

What is the principle of thermal paper? Will long-term contact with thermal paper really affect your health?

01

What is thermal paper and how does it work?

What we usually call printing is transferring ink to paper in a specific way, and finally presenting the required text or picture on the paper.

Inkjet printers and laser printers are the most commonly used types of printers in offices. Inkjet printers print by spraying ink droplets, while laser printers use electrostatic attraction to first use a toner cartridge (also known as a photosensitive drum) to absorb toner and then transfer it to paper.

However, the movie tickets, lottery tickets, shopping receipts and other documents we mentioned above are not printed in this way. Instead, they use a special material called "thermal paper".

This is very familiar, the locker receipts in shopping malls and supermarkets

Image source: Wikipedia

Compared with ordinary paper, thermal paper has an additional thin coating on the surface, which contains a special chemical substance called leuco dye.

Since the leuco dye is colorless, thermal paper looks no different from ordinary paper at room temperature. As the temperature rises, the leuco dye and acidic substances melt into liquids, and the molecules in the ingredients will produce chemical reactions, so the color will soon appear on the white paper. The color change of paper caused by a certain temperature is the reason why thermal paper gets its name.

Thermal paper, image source: pexels

Thermal paper alone is not enough. If you want to print text or graphics on its surface, you need a thermal printer. The internal structure of a thermal printer is very simple: there is no ink cartridge, the ink has been pre-coated on the thermal paper, and it mainly consists of two parts: the roller and the print head.

After putting the thermal paper into the printer, the thermal paper will continue to move forward under the drive of the roller, and when it touches the print head, it starts to work. If you look closely, you will find that there are many tiny semiconductor components on the surface of the print head, which can heat specific areas of the paper according to the text or graphics we want to print.

At the moment when the thermal paper comes into contact with the print head, the dye and acidic substances on the surface of the thermal paper will melt into liquid under the high temperature generated by the print head. Accompanied by a series of chemical reactions, the content we need will appear on the surface of the paper.

Printer dye box image source hippopx

02

Disappeared handwriting

Although thermal paper has the characteristics of fast printing speed and low noise, it also has a practical problem: after a certain period of storage, the writing on the thermal paper will gradually fade.

This is because at high temperatures, the hidden color dye on the thermal paper undergoes chemical changes to become another colored structure, and this structure is not stable and is easily affected by the external environment.

After a receipt is printed, it will come into contact with various chemicals in the air. These tiny chemical collisions may cause the dye on the thermal paper to return to a colorless state.

Image source: hippopx

In addition to these objective factors, there are also many ways to make fonts disappear through human factors. Thermal paper, as the name suggests, is a kind of paper that is sensitive to "heat". When we need the handwriting to disappear quickly, we can place the thermal paper in the sun or under a desk lamp. As long as the temperature reaches a certain condition, the unstable chemical properties will cause the handwriting to disappear.

Another method is to use a substance containing a large amount of organic solvents to remove the fonts on thermal paper. Organic solvents themselves are very effective cleaning agents. Commonly used perfumes and toilet water are also organic solvents.

03

Concerns from consumers

In recent years, thermal paper has caused many consumers to worry because it contains bisphenol A. Bisphenol A is an acidic substance, and the color of thermal paper is the result of a chemical reaction between bisphenol A and leuco dyes.

Studies have shown that bisphenol A on thermal paper can enter the human body through "touch". The latest experiments have confirmed that after long-term contact with thermal paper, the content of bisphenol A in urine will increase. Since the chemical structure of bisphenol A is similar to the estrogen secreted by the human body, estradiol, many people are worried that this substance will interfere with the endocrine system in the body, leading to precocious puberty and increasing the risk of disease.

It should be pointed out that the concentration of bisphenol A that enters the human body through thermal paper is very low, and there is currently no definite data to prove that it will have a negative impact on human health. However, in order to minimize the possible harm, many manufacturers have begun to use other acidic substances to replace bisphenol A.

It seems that thermal paper is a natural "intelligence tool", but if you really want to use this method to transmit secret intelligence, there is also a risk of leakage!

END

Review expert: Sun Yafei, Ph.D. in Chemistry from Tsinghua University

Tadpole Musical Notation original article, please indicate the source when reprinting

Editor/Heart and Paper